1. Field of the Invention
The present invention relates to a semiconductor device evaluation apparatus and particularly, to a semiconductor device evaluation apparatus for evaluating an electromagnetic near-field strength of a semiconductor device. The present invention further relates to a magnetic field sensor suitable for use in the semiconductor device evaluation apparatus.
2. Description of the Prior Art
EMI (electromagnetic interference) evaluation of electronic equipment is to measure an emitted far-field of the electronic equipment according to measurement methods stipulated in various kinds of standards and evaluate whether or not an emission quantity meets a standard. If the standard is not met, further detailed evaluation is performed at levels of a case and a print circuit board of the electronic equipment as evaluation objects in order to specify a problematic part in the equipment.
As a fundamental evaluation method, there can be named a method in which electrical parameters such as a current, a voltage and an electromagnetic near-field and the like at parts of an object for evaluation are measured by proper means and a part which has a possibility to cause a problem in terms of electromagnetic compatibility is thus specified. For example, in Japanese Patent Application Laid-Open No. 4-230874, there is disclosed a method in which a two-dimensional electromagnetic strength measurement apparatus is employed, a print circuit board built in electronic equipment is extracted therefrom, a magnetic field sensor is disposed in the vicinity of the print circuit board, a two-dimensional magnetic field distribution is measured in a plane which is parallel to the board and it is eventually evaluated that a part where a high magnetic strength is measured has a high possibility of being a noise source.
In such a conventional example, in many cases, there has been adopted a method in which, at first, a problematic part and a mechanism of a problematic circuit function are selected by narrowing candidates from a list thereof according to experiences and expertise of a person in measurement and an optimal EMC countermeasure is attained. For a countermeasure in an EMC, it is important to conduct non-contact measurement in order to suppress, to the lowest level possible, an electrical influence on a circuit function of the electronic equipment which is an evaluation object. When a semiconductor device itself (for example, a semiconductor package) as an object for evaluation is, in a non-contact manner, measured to specify an internal problematic part as in the case of electronic equipment, there arises a necessity for an electromagnetic sensor with a spatially high resolving power.
However, a practical electromagnetic sensor adaptable for a semiconductor device has not been known.
As a noise evaluation method of a semiconductor device, there is available a document: "Electromagnetic Emission (EME) Measurement of Integrated Circuits, DC to 1 GHz" IEC 47A/429/NP NEW WORK ITEM PROPOSAL, 1996.2, published by IEC in which a measurement method for emission noise from a semiconductor device is shown. Besides, there is also available a document: "Electromagnetic Compatibility to Measurement Procedures for Integrated Circuits" IEC 47A/428/NP NEW WORK ITEM PROPOSAL, 1996.2, published by IEC in which a measurement method for conduction noise which occurs in each pin of a semiconductor device is shown.
Two measurement methods for an emission noise from a semiconductor device package are shown. One will be shown below. A semiconductor device which is an object for evaluation is mounted on a surface of a print circuit board and peripheral circuitry for operating the semiconductor device is constructed on the rear surface thereof. The print circuit board is fixed on a plane in the top portion of a TEM cell so that a surface of the print circuit board on which a semiconductor device is mounted resides in the inside of the TEM cell. One end of the TEM cell is constructed as a reflection-free terminal and the other end connected to a spectrum analyzer, and thereby emission noise from the semiconductor device only can be measured excluding influences from the peripheral circuitry.
A second method will be shown below. A semiconductor device as an object for evaluation is mounted on a surface of a print circuit board and peripheral circuitry for operating the semiconductor device is constructed on the rear surface thereof. The print circuit board is disposed with the surface on which the semiconductor device is mounted facing upward and a shielded loop constructed from a semi-rigid coaxial cable is arranged above the print circuit board. The vicinity of the semiconductor device is scanned with the shielded loop along a plane parallel to the print circuit board by a scan mechanism and thereby emission noise from the semiconductor device only can be measured. In this case, the maximal value of outputs at measurement sites is evaluated as a problematic site to specify.
Then, a measurement method for conduction noise which occurs in each pin of a semiconductor device package will be shown below. A structure comprises a test board for mounting a semiconductor device which is an object for evaluation and a main board for connecting the test board and a spectrum analyzer thereby. The semiconductor device is mounted in the center of the circular test board and the test board is attached to the main board in the center thereof. Interconnects are provided on each of the two boards radially toward the outside of the board and conduction noise from the pins of the semiconductor device is measured by the spectrum analyzer which is connected to the pins through connectors of a coaxial type mounted in the vicinity of the outer periphery of the main board.
As other examples, the following methods are named. For example, in Japanese Patent Application Laid-Open No. 64-65466, there is disclosed an identification method for an electromagnetic field noise generating part in which a reference plane is imagined which intersects electronic equipment, an arbitrary plane which is in parallel with the reference is scanned with an antenna, strengths of electromagnetic field noise and noise generating sites are sampled, and thereby a generation distribution map for electromagnetic noise of the electronic equipment as viewed from the arbitrary plane set in advance is expressed in the form of a contour map. Besides, in Japanese Patent Application Laid-Open No. 5-119089, there is disclosed an electromagnetic radiation visualization apparatus, in which a variable-length dipole antenna 3 of a measurement unit 1 is fixed in length which matches a measurement frequency and the antenna 3 is moved by a three-dimensional movement mechanism 4 in an anechoic electromagnetically chamber 7 while scanning. At this point, the interior of the electromagnetically anechoic chamber 7 is optically made dark and a brightness of a lamp 2 which is proportional to an electric field strength at each measurement site is recorded by a sterocamera 5 with exposure. Furthermore, in Japanese Patent Application Laid-Open No. 6-58970, there is disclosed an invention having an object to provide an EMI measurement apparatus which can three-dimensionally measure noise along X-Y-Z directions on the front side of a print wiring board on which electronic parts with much of unnecessary radiation are mounted, and which can two-dimensionally measure noise along X-Y directions on the rear side thereof. This is an EMI measurement apparatus which has a construction in which a print wiring board is set to an antenna for measuring an interference in which winding coils are arranged in an array and a magnetic near-field probe is mounted on the fore end arm of a robot which can be driven along X-Y-Z directions on the front side of the print wiring board in order to measure a noise generating source of the print wiring board on which an electronic part which is rich in unnecessary radiation is mounted, whereby a distribution of magnetic field strengths in unnecessary radiation on both sides, front and rear, is measured. In addition, in Japanese Patent Application Laid-Open No. 9-80098, there is disclosed an EMC probe, by which a spatial resolving power is increased and a measurement band region is sufficiently secured. This comprises a flexible board whose surface is insulated and a winding 11 with a single turn or a plurality of turns for detecting a magnetic near-field vector of an object for measurement, while being disposed obliquely, the winding being constructed from a metal thin film formed in a plane on the board.